1. Field of the Invention
This invention relates to a method of manufacturing a semiconductor device having a thin film resistor, and particularly to a method of etching a metallic thin film on the thin film resistor.
2. Description of the Related Art
A conventional method of manufacturing a CrSi resistor device including a CrSi resistor and a TiW barrier metal will be explained referring to FIGS. 1A to 1D. First, as shown in FIG. 1A, a CrSi film is deposited on a silicon substrate 101 through a silicon oxide film 102 interposed therebetween, and is patterned in to a shape of a CrSi resistor 103. Then, as shown in FIG. 1B, a TiW film 104 as barrier metal is deposited to cover the CrSi resistor 103, and an Al film 105 is deposited as electrodes. After that, as shown in FIG. 1C, the Al film 105 is patterned by etching using a photo-resist 106 as a mask. As shown in FIG. 1D, an unnecessary part of the TiW film 104 is further removed by wet etching using the photo-resist 106 as a mask again.
FIG. 2 is an enlarged view showing a portion around the CrSi resistor 103 formed by the conventional method described above. As shown in the figure, the conventional method is accompanied by Al over-hanging such that the Al film 105 is inversely tapered by the wet etching for the TiW film 104, and TiW under-cut such that the etching of the TiW film 104 progresses under the Al film 105. As a result, the Al film 105 and the TiW film 104 form an inversely tapered cross-sectional shape as a whole. The inversely tapered cross-sectional shape adversely affect a shape of an intermediate insulation film which covers the CrSi resistor device, and further affects not only a shape of a wiring pattern formed on the insulation film but also a shape of a protective film for covering the wiring pattern. This may result in breakage of the wiring pattern and cracks in the protective film.
Further, as shown in FIG. 3, when the under-cut amount of the TiW film 104 is large, it becomes difficult for an intermediate insulation film 108 to fill the under-cut portion. This results in deterioration of step-coverage, and allows invasion of water or the like. As a result, the reliability of the device is lowered. Incidentally, FIG. 3 omits the over-hanging portion of the Al film 105.